1. Field of the Invention
The Invention is drawn to a method and apparatus for removing ammonia from the air which is exhausted from animal rearing facilities such as those used for poultry and swine.
2. Description of the Prior Art
One of the major problems encountered in raising livestock such as hogs, chickens, turkeys or laying hens under confined conditions is ammonia volatilization, the production of excessive levels of ammonia gas (NH3). For example, in poultry houses, as volatilization occurs, ammonia levels can reach as high as 100–200 ppm. Scarborough (Delaware Agric. Exp. Stn. Prog. Rep., NE8, 1957) and Valentine (Br. Poultry Sci. 5:149–159, 1964) both observed ammonia levels in the 60 to 70 ppm range in the atmosphere of poultry houses. Ammonia levels reaching as high as 100 ppm in commercial poultry houses have also been reported (Anderson et al., Poult. Sci. 43:305–318 (1964)).
Ammonia generation and its associated odor present not only a source of complaints from communities which neighbor animal production facilities, but exposure to excessive ammonia levels also presents serious health problems for both the animals and their human handlers, and atmospheric ammonia contributes to environmental problems. Anderson et al. demonstrated that when chickens, turkeys, guinea pigs, or mice were exposed continuously to 20 ppm ammonia, gross or histopathological signs of damage to the respiratory tract occurred after six weeks (Avian Dis. 8:369–379, 1964). They also found that chicks exposed to 20 ppm ammonia for 72 hours were much more susceptible to Newcastle Disease than controls reared in ammonia-free environments. Although all of the chickens had been exposed to the Newcastle Disease virus, only 40% of the chickens in the ammonia-free environment were infected, whereas 100% of the chicks were infected when exposed to ammonia. They indicated that these results may have been due to damage to the mucous lining of the respiratory tract. High levels of ammonia have also been shown to enhance the multiplication of Mycoplasma gallisepticum in the respiratory tract of chickens (Sato et al., Natl. Inst. Anim. Hlth. Qt., Tokyo, 13:45–53, 1973). Charles et al. (British Poultry Science 7:177–187, 1966) found that keratoconjunctivitis developed in hens exposed to 100 ppm ammonia after six weeks, and egg production was depressed.
Similar effects have been observed in swine. High atmospheric ammonia levels in swine rearing facilities have been shown to have a significant negative effect on feed consumption, feed conversion and daily weight gain in pigs. Strombaugh et al. found that high levels of ammonia adversely affected feed consumption and weight gain in pigs (J. Anim. Sci. 28:844, 1969). High levels of atmospheric ammonia in swine rearing facilities have been shown to aggravate swine respiratory problems, increasing their susceptibility to micro-organisms responsible for such respiratory problems, such as Pasteurella multocida. Ammonia also increases the susceptibility of four week old pigs to conchal atrophy. Likewise, high ammonia levels in swine facilities may play a significant role in the development of atrophic rhinitis.
In Europe, COSHH (Control of Substances Hazardous to Health) has set the limit of human exposure to ammonia at 25 ppm for an eight hour day and 35 ppm for a 10 minute exposure (Williams, Proc. Ark. Nutrition Conference, Fayetteville, Arkansas, pp. 14–29, 1992). With current production practices, these levels are often exceeded in broiler houses.
Another detrimental aspect of NH3 volatilization is the effect on acid rain, with studies indicating that atmospheric ammonia pollution plays an important role in acid rain pollution. The reportedly dominant source of atmospheric NH3 in Europe is livestock waste, with long term trends showing a 50% increase in NH3 emissions in Europe from 1950 to 1980. Ammonia raises the pH of rainwater, which allows more SO2 to dissolve in it. Ammonium sulfate then forms, which oxidizes in the soil, releasing nitric and sulfuric acid. This produces two to five times the acid input to soils previously described for acid atmospheric deposition, resulting in extremely low pH values (2.8–3.5) and high levels of dissolved aluminum in non-calcareous soils. Ammonia volatilization can also contribute to eutrophication. Reports show that nitrogen deposited via wet fallout tripled in Denmark from 1955 to 1980, corresponding to increases in nitrogen losses from agricultural operations during this period. The rising levels of nitrogen in the fallout have also been linked to the NH3 content in Danish streams.
Ammonia volatilization also greatly increases atmospheric N fallout, which contributes to eutrophication. Nitrogen deposited by wet fallout tripled in Denmark between 1955 to 1980 and corresponded to N losses from agriculture during the same period. Rising levels of N in the fallout have also been shown to be highly correlated to the NO3 form nitrogen content in Danish streams.
Atmospheric ammonia can also result in the formation of ammonium nitrate particles in the air. These particles, which are usually less than 2 microns in size, contribute greatly to small airborne particles referred to as PM-10's (particulate matter less than 10 microns).
A number of strategies for controlling odor, and specifically reducing ammonia volatilization, from animal production facilities have been proposed. There are several litter amendments currently on the market which supposedly reduce ammonia volatilization. Among these are MLT (Multi-Purpose Litter Treatment), PLT (Poultry Litter Treatment), De-odorase, and Ammonia Hold.
Moore, disclosed a number of different processes for inhibiting NH3 volatilization from poultry litter, and from manure or urine collected from animal production facilities, by treatment with alum (aluminum sulfate), aluminum chloride, or aluminum nitrate (U.S. Pat. Nos. 5,961,968; 5,865,143; 5,914,104; 5,890,454; and 6,346,240).
In addition to processes for treating litter and animal waste, still other processes have been developed for the treatment of air exhausted from animal containment buildings. Scrubbers and/or biofiltration units have been described for use in combination with the ventilation systems of these buildings, such as described by Mackin et al. (U.S. Pat. No. 5,666,905), Ferranti (U.S. Pat. No. 6,358,729), Cox et al. (U.S. Pat. No. 5,017,203), Allen (U.S. Pat. No. 6,534,306), and Firth (U.S. Pat. No. 5,738,713).
However, despite these advances, the need remains for improved facilities and methods for rearing animals under conditions which reduce the levels of volatilized ammonia in the air from animal production facilities.